Wallboard for many years has been the standard material used to erect interior walls in the construction of buildings. Wallboard is installed in large panels that are nailed and glued to the wall studs and fitted together until the wall section is covered with joint compound, then with tape, and then the taped joints and all nails and screws are covered with joint compound. Upon hardening, the joint compound is sanded smooth so that it is imperceptible under paint or other wall covering.
Joint compounds generally contain a resinous binder, limestone, clay, mica, stabilizer, lubricant and thickener as the principle ingredients that are mixed with water to form a workable mass that is applied to the wall by troweling.
The water soluble polymer used to thicken and stabilize joint compounds is typically a cellulose ether, e.g., methylhydroxypropylcellulose, hydroxyethylcellulose and derivatives thereof. The thickener system is usually from 0.3% to 0.7% of the total weight of the finished joint compound. Water is typically 28-32% of the formulation weight, giving the combination of desirable working properties and reasonable manufacturing cost efficiency. Increasing the water content to levels above the typical range, i.e., above about 32%, will, of course, result in cost savings for the manufacturer, but, upon drying, cracking and shrinkage will likely be unacceptably worsened. On the other hand, very often, thickeners impart excellent working properties to joint compounds but may suffer in that the joint compound viscosity is somewhat lower than desired. Decreasing the water level below the typical range in order to increase product viscosity would be prohibitively expensive. Increasing the thickener level would be even more expensive. Methods to increase joint compound viscosity without increasing thickener levels or decreasing water levels are always an objective in the industry.
Improvements in joint compound compositions are known from U.S. Pat. Nos. 3,891,582, 4,558,079 and 3,835,074. Thickening combinations of cellulose ethers and polyacrylic acid are known from U.S. Pat. Nos. 4,720,303, 4,846,889 and 4,594,108.
Yet in spite of what was known concerning joint compound formulations, portland cements, flocculation agents and the use of polyacrylic acid compositions, it remained for the present invention to further advance the state of art for high productivity joint compound compositions.